The problem that is currently facing the semiconductor industry is how to planarize a probe card to a wafer during testing of individual die on that wafer. If planarization is not achieved, then some probe needles apply more pressure to corresponding lead pads on the die, while others apply less. This at a minimum could result in incomplete electrical interfacing with the die so that the die tests bad, or at worst that the lead pads to which more pressure is applied are physically damaged making it impossible to use the die in a finished product.
What is currently done in the industry is to dock the tester with the prober, bringing the probe needles into contact with a test die on a single wafer or a single wafer in a cassette of wafers. The system is then undocked and the individual lead pads on the test die are optically examined to determine if more pressure has been applied to some lead pads on that die. This is done by looking for scratches and possibly indentations in the individual lead pads. Since the lengths of the probe needles are adjusted to be within 10 microns of each other, typically the greatest pressure will be applied to adjacent lead pads on one side of the test die and the least pressure will be applied to the lead pads that are 180.degree. displaced from those that experienced the greatest pressure. Based on those observations, the operator makes an educated guess as to how much adjustment, and in what direction, is needed to planarize the probe card to the wafer. The probe card is then shimmed accordingly and the other dies on the wafer, or all wafers in the cassette, are tested. Thus, it is necessary to repeat this process each time the wafer, or cassette of wafers, is changed.
Also, since the planarization process in the prior art is performed when the test head is separated from the prober, there is no contact between the interface card, the pogo ring, the probe card, the probe needles and the wafer. Thus, when docking is achieved everything is changing due to internal stresses and moments, there is a high probability that the probe needles are changing position as well.
Of course, this process is aggravated by the fact that there is usually very little space between the prober and the test head. Thus, in the prior art, planarization is accomplished with the prober and test head un-docked. The prior art does not include a way to perform planarization after docking has been achieved.
To insure that the probe card and probe needles are planarized with the wafer after docking is achieved, a system is needed that performs planarization after docking has been achieved. The present invention provides such a system.